Information handling systems play a vital role in our modern society. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated.
The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information-handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
A computer system, which is one common type of information handling system, may be designed to give independent computing power to one or a plurality of users. Computer systems may be found in many forms including, for example, mainframes, minicomputers, workstations, servers, clients, personal computers, Internet terminals, notebooks, personal digital assistants, and embedded systems.
Information handling systems often include components that require a regulated power supply. FIG. 1 illustrates relevant components of an information handling system 10 having a CPU 12 coupled to a memory 14 that stores instructions executable by the microprocessor. Information handling system 10 includes an electric fan motor 16 that turns a fan blade (not shown) for cooling the CPU 12 during operation thereof. CPUs require active cooling to operate in a thermal envelope recommended by the manufacturer thereof. Fans are the preferred means for maintaining CPU temperature within the recommended thermal envelope. Ideally, the maximum airflow (fan is fully on) provides the best cooling results. However, it is desirable to be able to gradually vary the fan speed according to the cooling needs in order to save power. Additionally, reducing fan speed reduces acoustic noise produced by the cooling fan. The fan speed can be varied by varying the voltage provided to the power input node of the electric fan motor 16.
Fan speed depends on the magnitude of voltage provided to motor 16. Information handling system 10 includes a circuit for regulating the power provided to electric fan motor 16. The circuit includes a power management circuit (PMC) 18 and power field effect transistor (FET) 20 coupled between the electric motor 16 and PMC 18. More particularly, the output of PMC 18 is coupled to a gate-input node of FET 20. The source node of FET 20 is coupled to a first power supply having a voltage VCC1, while a drain node of FET 20 is coupled to a power input node of motor 16.
PMC 18 generates a square wave signal, the duty cycle of which depends upon a control signal provided to PMC 18. FIG. 2 illustrates an exemplary square wave generated by PMC 18. The square wave shown in FIG. 2 varies between VCC2, the voltage of a second power supply provided to PMC 18 in FIG. 1, and ground. VCC2 may be distinct from VCC1. The first power supply is capable of providing high current power to fan motor 16 when compared to the current that is provided by the second power supply. As noted above, the duty cycle depends upon the control signal provided to PMC 18. The period of square wave shown in FIG. 2 remains constant notwithstanding a change in the duty cycle in response to a change in the control signal provided to PMC 18.
The square wave signal generated by PMC 18 is provided to the gate-input node of power FET 20. When the voltage of the square wave signal is at VCC1, FET 20 activates thereby coupling the first power supply to the power-input node of fan motor 16. In response, a shaft (not shown) of motor 16 rotates thereby turning a fan blade (not shown) which in turn produces airflow over microprocessor 12. When the voltage of the square wave signal provided to the input gate of FET 20 is at or near ground, FET 20 turns off thereby disconnecting the first power supply from the input node of fan motor 16. In response, the rotational speed of the motor shaft begins to slow and may even stop until FET 20 is again activated by the square wave.
The rotational speed of the fan motors"" shaft depends upon the duty cycle of the square wave provided to FET 20. The higher the duty cycle the higher the average rotational speed of the shaft. To obtain the highest average rotational speed, the duty cycle of the square wave should be 100%. With a 0% duty cycle, no power is provided to fan motor 16, and the shaft thereof does not rotate. For duty cycles between 0 and 100%, the average rotational speed of the motors"" shaft varies accordingly.
The constant coupling and decoupling of the first power supply to the power input node of fan motor 16 according to the square wave provided to the gate input node of FET 20, stresses fan motor 16 such that fan motor 16 may eventually and prematurely fail. Additionally, the constant coupling and decoupling of first power supply to fan motor 16 corrupts logic within motor 16 that generates a tachometer output signal of fan motor 16 which may be used to determine whether rotational speed of the shaft is set at a desired rate.
Disclosed is a circuit for regulating a power supply. In one embodiment, the circuit includes a signal generator for generating a square wave signal that varies in magnitude between a first voltage and a second voltage, and a voltage regulation circuit. A duty cycle of the square wave generated by the signal generator varies according to a signal provided to the signal generator. The voltage regulation circuit, coupled to the signal generator, outputs a DC voltage in response to the circuit receiving the square wave signal. The magnitude of the DC voltage varies between the first voltage and a third voltage, wherein the third voltage is greater than the second voltage, and wherein the magnitude of the DC voltage varies directly with the duty cycle of the square wave signal.